<?php
/**
 * Created by PhpStorm.
 * User: zhangrongxiang
 * Date: 2018/2/12
 * Time: 下午10:19
 */

$arr = [
	"C"      => "I am the GOD",
	"PHP"    => "PHP is the best language int the world",
	"Python" => "Life is short, I use Python",
	"Java"   => "Write once, run anywhere",
	"Go"     => "better C",
	"ZING"   => null
];
print_r(array_keys($arr));
print_r(array_keys($arr,null));
print_r(array_keys($arr,NULL,true));
print_r(array_keys($arr,'better C',true));